Windows 12 could see a substantial system redesign in order to include a more AI-centric user experience. The start button could thus be replaced with Copilot AI, which is already available as a preview version in the latest Windows 11 update.
That would be because Cortana was hot garbage at doing anything and was significantly slower than just typing my query by hand.
If they built an assistant that was worth half a fuck maybe we might have used it now and then. I'm not very confident that Copilot is that. But it's going to be more useful than Cortana was almost no matter what they do with it.